<!DOCTYPE html>
<html>
<head>
  <style>
    body {
      width: 300px;
      height: 300px;
      overflow: hidden;
      margin: 0;
      padding: 0;
    }
    button {
      display: block;
      margin: 0;
      padding: 0;
      border: 0;
      width: 100px;
      height: 50px;
      position: absolute;
    }
    #b1 {
      left: 0;
      top: 0;
      background-color: #090;
    }
    #b2 {
      left: 0;
      top: 150px;
      background-color: #900;
    }
  </style>
</head>
<body><button id="b1" aria-label="Button 1"></button><button id="b2" aria-label="Button 2"></button></body>
